1. Field of the Invention
The invention relates to a marking unit for marking a material web that can be wound up onto a core utilizing a winding device, and also to a corresponding marking method for this purpose.
2. Description of Background
In the web processing and producing industry, such as the paper industry, for example, material webs are wound onto a core by means of winding devices at various stages of production. In this case, the winding devices are often known as reelers, in which the core with the material web already wound up, referred to as a reel, is in contact with one or more pressure rolls, a nip formed between the reel and the pressure roll.
During the winding of the material web, for example, because of changes in web tension upstream of the nip or because of the elasticity of the material web or because of the action of force in the nip, positional displacement of the material web wound onto the core can occur. Such positional displacement can lead to winding defects such as creping folds or breakage of the material web.
In order to detect positional displacements, manual methods of marking are used as required, in which radial lines are applied successively to the end of the part of the material web already wound and the change in the lines is observed over the course of further winding operation and subsequently analyzed. If, in the ideal case, no positional displacements have taken place, then the lines applied would ideally result in a radial line over the entire thickness of the wound material web. However, due to positional displacement, a line with a J shape, what is known as a J-line, is established over the thickness of the wound material web. A highly deformed J-line results when severe positional displacements occur. Furthermore, the wound tension is incorporated in the shape of the J-line. Thus, the J-line is, for example, deformed less severely if the web tension is increased before reeling, that is to say when harder winding is carried out.
The disadvantage with the known mechanical methods is that the manual application of the marking line is dangerous for the person carrying it out as a result of the proximity to the rotating reel. Furthermore, the reproducibility of the manual marking depends to a great extent on the skill of the person carrying it out. Moreover, the manual methods cannot be applied in a prophylactic manner since the winding quality can only be determined retrospectively.